Propulsion installations for boats, more particularly for high-speed launches

ABSTRACT

The specification discloses a very compact installation for a high-speed launch, such installation comprising a main internal combustion power unit and an auxiliary power unit, each unit having a drive shaft extending into a reduction gear mechanism which also has an output shaft driving a screw, the reduction gear mechanism being arranged so that the auxiliary power unit can selectively either (a) drive water and oil pumps of the main power unit to preheat the unit, (b) drive the main power unit to start the same, or (c) drive the screw during low speed manoeuvres.

Umted States Patent 11 1 1111 3,872,675 Amiot Mar. 25, 1975 1 PROPULSION INSTALLATIONS FOR 3,230,698 17966 Nettles 60/6 3,601,980 8 1971 Faber..... 60/11 BOATS MORE PARTICULARLY FOR 3,683,719 8/1972 Gros 60/11 [76] Inventor: Felix Amiot, 2, rue Georges leygues (16c), Paris, France [22] Filed: Sept. 15, 1972 [21] Appl. No.: 289,264

[30] Foreign Application Priority Data Jan. 13, 1972 France 72.01106 [52] 11.8. CI. 60/718, 74/661 [51] Int. Cl. ..F01b 21/00 [58] Field of Search 60/718, 717, 716; 74/661;

[56] References Cited UNITED STATES PATENTS 2504.833 4/1950 Hann 60/6 X 17b l3b 1 19b HIGH-SPEED LAUNCHES Ill Prinmry E.\'aminerMartin P. Schwadron Assistant Examiner-Allen M, Ostrager Almrney, Agent, or Firm-Larson, Taylor & Hinds [57] ABSTRACT The specification discloses a very compact installation for a high-speed launch, such installation comprising a main internal combustion power unit and an auxiliary power unit, each unit having a drive shaft extending into a reduction gear mechanism which also has an output shaft driving a screw, the reduction gear mechanism being arranged so that the auxiliary power unit can selectively either (a) drive water and oil pumps of the main power unit to preheat the unit, (b) drive the main power unit to start the same, or (c) drive the screw during low speed manoeuvres.

7 Claims, 19 Drawing Figures Lzb PATENTEDHARZS i975 SHEET 02 0F 14.

Fig.1c1

PATENTED 2 SHEET O70F14 Fig.4

PATENTEU 2 5 SHEET GBUF 14 Fig.4cl

PATENTEDHARZSIQYS SHEET l0 UF 14 Fig.6

PATENTED 7 872,675 SHEET 1 1 0F 14 Fig. 7

SHEET 12 0F 14 Fig.8

PATENTEU W 2 5 I975 SHEET l3 UF 14 PROPULSION INSTALLATIONS FOR BOATS, MORE PARTICULARLY FOR HIGH-SPEED LAUNCHES BACKGROUND OF THE INVENTION This invention relates to propulsion installations for boats, of the type which develop a relatively high power (above 1,000 HP. and up to 10,000 HP, and even several tens of thousands horse-power); the invention relates more particularly because this would appear to be the most advantageous application but not exclusively to propulsion installations of this type intended for high-speed launches or patrol-boats, i.e., boats requiring powerful propulsion installations with only limited space available for their accommodation.

Boat propulsion installations of this type generally comprise, inter alia, a power unit coupled to a reduction gear mechanism, the output shaft of which is coupled to a propulsion means such as a screw, the power unit being equipped with auxiliaries, some of which are pumps (cooling liquid pumps, lubricating pumps), which contribute more particularly by their operation to bringing the power unit up to the required operating temperature during the time from the start order until the operation of the main engines at the required temperature.

Propulsion installations of this kind should advantageously satisfy in the best possible way a number of criteria, some of which are mechanical, others of a marine nature while yet others are of an economic nature or tactical or strategic in the case of propulsion installations for naval vessels (i.e., particularly high-speed surveillance and attack launches).

Of these criteria, the following would appear to be the most important: the weight and size reduction of the means required for starting the power unit; preheating of the power unit before starting; the possibility of carrying out harbour manoeuvres, i.e., low-speed manoeuvres, under conditions which do not adversely affect the operation of the power unit, such harbour manoeuvres always being necessary between the quayside situation and the situation from which the boat can use a required speed without inconvenience; reduction of the time required for bringing the boat to the operational condition, i.e., the time between the moment at which the start order is given (boat at quayside with propulsion installation completely stopped) and the moment when preheating of the power unit is complete and the harbour manoeuvres have been carried out, and the boat is capable of using the required speed and undertaking the mission entrusted to it; at the end of the stage of bringing the boat to the operational condition, the stoppage of the maximum possible number of movable components of the installation which were involved in bringing the boat to the operational condition but which no longer have to play any function beyond that stage, i.e., within the normal range of operating speeds of the said installation; accessibility and convenience of inspection and removal of the main components of the reduction gear mechanism; and, in the (special and frequent) case in which the power unit of the installation comprises a plurality of engine elements coupled to a common reduction gear mechanism whose output shaft forms the single drive shaft of the installation, maximum independence of the said engine units as regards normal operating and starting.

It is precisely the main object of this invention simultaneously to satisfy the above criteria to a wide extent, since this was not the case with propulsion installations of the type hitherto proposed, i.e., those in which starting of the. power unit is carried out by an installation for the injection of compressed air into the cylinders of the power unit, such installation comprising compressors, air cylinders, valves, control units, and so on, of appreciable weight and size; the same applies to installations of the kind equipped with a separate propulsion unit for harbour manoeuvres, this unit in no way contributing to the otherstages of the procedure for bringing the installation to the operating condition (preheating and starting of the power unit in particular).

SUMMARY AND DESCRIPTION OF INVENTION The invention provides a propulsion installation comprising:

a power unit; a reduction gear mechanism; a primary input shaft of the reduction gearmechanism drivingly connected with said power unit; an output shaft of the reductiongear mechanism arranged to drive prop ulsion means; wherein the improvement comprises the provision of:

an auxiliary engine; a secondary input shaft of the reduction-gear mechanism arranged to be driven by the auxiliary engine; means to decouple the said output shaft from the primary input shaft; said reduction gear mechanism including means to drivingly connect the secondary power input shaft to the output shaft with such output shaft decoupled from the primary input shaft; and means including a freewheel device to drivingly connect the secondary power input shaft to the primary input shaft for starting of the power unit, said freewheel device permitting transmission of torque from the secondary power input shaft to the primary power input shaft to rotate a shaft of the power unit in the direction in which such shaft is rotated for starting of the power unit.

In the advantageous case in which the installation power unit comprises a plurality of engine units coupled respectively to as many input shafts provided for this purpose in the reduction gear mechanism, the gear train and the coupling means of the said reduction gear mechanism are so arranged for starting as to allow the user selectively to couple the power take-off shaft driven by the auxiliary engine to any ofthe input shafts associated with the said engine units so that the engine units in question can then be started successively.

When the installation power unit consists of only two engine units, the reduction gear mechanism comprises for the purposes of starting one or other of the said engine units, a transmission mechanism comprising gearwheels mounted on a rocking support which can be brought from a neutral position into one or other oftwo end positions in which one of two output gearwheels of the said transmission mechanism meshes with one or other of the starting means for the said engine units.

Irrespective of which embodiment is adopted, the main feature of the invention enables the auxiliary engine associated with the propulsion installation to perform a double role, i.e., enables the auxiliary engine to carry out the harbour manoeuvres on its own and carry out starting of the power unit of the propulsion installation at the required time.

The marine propulsion installation according to the invention may also have other advantages by applying to it, in addition to the main feature above, one or more of the following additional features which form part of the invention and which will now be discussed more exp QitlX- According to a first additional feature, the gear train and transmission means of the reduction gear mechanism are also so arranged as to allow selective coupling of the power take-off shaft driven by the auxiliary engine to some or all of the accessories of the power unit (more particularly lubricant and cooling liquid pumps) which, by their operation, are adapted to assist the power unit in running up to temperature, this first additional arrangement allowing the auxiliary engine provided in the propulsion installation to perform a third beneficial role.

Preferably, the said auxiliaries are driven at areduced speed in relation to their normal operating speed.

According to a second additional feature, some of the auxiliaries of the power unit, more particularly those assisting in running the power unit up to temperature, are borne by the reduction gear mechanism and driven by the latter, thus facilitating their inspection and maintenance, simplifying their drive system and making any repairs more convenient.

According to a third additional feature, the reduction gear mechanism of the installation comprises a casing having a joint plane at the level of each input or output shaft leading to the said reduction gear mechanism so that it is a simple matter to expose and repair at each of its levels the essential components of the power transmission at the level in question, inspection bellhousings or covers advantageously being provided in the walls of the said casing at the end of each line of shafting, said bell-housings or covers straddling the joint planes of the casing and, in the casing of bellhousings, also protecting some of the components of the reduction gear mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 is a highly diagrammatic perspective view of the essential elements of a propulsion installation according to the invention for a high-speed launch, said installation comprising a power unit consisting of two superposed engine units;

FIGS. 1a and lb are more detailed perspective views respectively in right-hand and left-hand three-quarter view showing a reduction gear mechanism belonging to this installation;

FIG. 2 is a perspective view of the complete gear train and transmission and coupling elements housed in the casing of the said reduction gear mechanism;

FIGS. 2a and 2b are elevations of two transverse lines of shafting of the reduction gear mechanism corresponding respectively to the bottom engine unit and the top engine unit of the installation power unit;

FIGS. to 2fillustrate details of FIG. 2 respectively in the direction of the arrows F0 to Ff;

FIG. 2g is a section of the said reduction gear mechanism in elevation;

FIG. 2h is a similar view to FIG. 2 and bears the reference of all the internal components of the reduction gear mechanism;

FIG. 3 shows in the same conditions the same elements of the reduction gear mechanism as FIG. 2, but the in this FIG. 3 double arrows show those of the said elements which are in motion during the preheating procedure of the power unit;

FIG. 4 is a similar view to FIG. 3 except that double arrows show the elements which are in motion on a harbour manoeuvre accompanied by simultaneous preheating of the power unit;

FIG. 4a is a similar view to FIG. 4 but differs from FIG. 4 in that further double arrows show the elements which are in movement in a harbour manoeuvre carried out without preheating of the power unit;

FIG. 5 is a similar view to FIG. 3 except that double arrows show the elements which are in movement during starting of the top engine unit of the power unit;

FIG. 6 a view similar to FIG. 5 but differs from FIG. 5 in that double arrows show the elements which are in movement on starting of the bottom engine unit of the power unit;

FIG. 7 a similar view to FIG. 3 but differs from FIG. 3 in that further double arrows show the elements shaded grey are those which are in motion when the two engine elements of the power unit are in operation;

FIGS. 8 and 9 are views similar to those above wherein double arrows indicate the components in motion illustrating, respectively, propulsion of the boat by the bottom engine unit on its own and by the top engine unit on its own, and

FIG. 10 differs from FIG. 9 only in that the bottom engine element is not only stopped but also under repair The high-speed launch propulsion installation shown diagrammatically in FIG. 1 comprises essentially a drive unit 1 formed from two superposed engine units 10 and 1b each having their own output shaft 20 and 2b respectively; a reduction gear mechanism 3 to which the output shafts 2a and 2b of the engine units la and lb are coupled, and a single output shaft 4 of which is coupled to the installation screw shaft 4a, preferably through a resilient coupling system; an auxiliary engine 5 coupled, for example via cardan shaft 6, to a power input shaft or secondary power shaft 6a which extends to the interior of the reduction gear mechanism 3; and a number of accessories, including accessories for bringing the power unit 1 to operating temperature, comprising, in the case of each engine unit, at least one cooling freshwater pump 7 and at least one circulating and lubricating oil pump 8, all these pumps being carried and driven by the reduction gear mechanism 3.

The engine unit 1 is preferably constructed in accordance with the French Pat. application filed by the same applicant on 23rd Aug., 1971 under the number 7l-30,52l for Improvements in and relating to propulsion installations for vehicles or vessels, more particularly for boats, new French Pat. No. 2,151,163 the said power unit then being formed from two superposed diesel engine units la and lb with turbocompressors and each comprising ten pairs of horizontal opposed cylinders. In these conditions each engine unit can develop a power of the order of 4,000 to 5,000 HP. and in this particular case this results in the complete power unit developing a total power of the order of 8,000 to 10,000 H.P., although this is of course only an example and without departing from the scope of the invention it would be possible to use power units developing a much higher total power.

The auxiliary engine 5 is preferably a diesel piston engine of a power of the order of 200 to 300 H.P., and this auxiliary engine may also be used if required to drive an electrical generator feeding the auxiliary equipment.

The reduction gear 3, which is shown in perspective at two different angles in FIGS. 1a and lb, comprises generally a casing 9 formed from four superposed elements which are connected detachably in three horizontal joint planes p (FIG. la), which from top to bottom are respectively situated at the level of the line of shafting L2b of the top element, L2a of the bottom engine unit and L4 of the reduction gear output.

The driving torque produced by the bottom engine unit la and collected at the output shaft 2a of the said engine unit is transmitted through a releasable coupling device a to a first input shaft 2a1 belonging to the line of shafting L2a and entering the reduction gear casing 9.

The driving torque produced by the top engine unit 1b and collected from the output shaft 2b of said engine unit is transmitted via a doubletoothing coupling 10b similar to coupling 10a to a second input shaft 2b1 belonging to the line of shafting L2b and entering the reduction gear casing 9.

At the opposite end to the output shaft 4, a control box 11 is provided at the end of the shafting line L4 for varying the pitch of the boat screw.

Detachable bell housings or covers co-axial with the shafting lines are also provided for ease ofremoval and installation on the lateral walls of the casing 9 through which the lines of shafting extend, and the following are examples of these:

on the line of shafting L2a: a cover 12a on the input shaft side 2111 and a bell 130 on the opposite side;

on the line of shafting L2b: a cover 12b on the input shaft side 2b1 and a bell 13b on the opposite side; and on the line ofshafting L4: a cover 14 which forms a fixing flange on the control box side 11 and a cover 15 on the opposite side.

A general structure of this kind for the reduction gear mechanism 3 makes inspection and any repaid of the internal elements of the mechanism very simple and rapid for the following reasons:

In the event of trouble with the elements housed in one of the bells 13a or 13b it is only necessary to remove the bell in question to gain access to the elements.

In the event of trouble on the top line of shafting L2b, coupling 10b is decoupled and bell 13b and cover 12b are removed, whereupon the fixing elements of the top element of the casing 9 are removed to release the said top element in the upward direction, access then being possible from the top to the interior of the reduction gear mechanism at the line of shafting L2b.

In the event of trouble on the bottom line of shafting L2a, the two couplings 10a and 10b are decoupled, bell 13a and cover 12a are removed, whereupon the fixing means of the casing elements connected in this joint plane are removed so that the two casing elements situated above the said joint plane can be released as a unit in the upward direction, then giving access from the top to the interior of the reduction gear mechanism at the level of the line of shafting L2a.

Finally, in the event of trouble at the level of the line of shafting L4, i.e., the screw shaft line, the covers 14 and I5 are removed and the screw pitch control box 11 is secured and the fixing means of the bottom casing elcment are removed so that the said bottom casing element can be released in the downward direction, thus giving access from above to the interior of the reduction gear mechanism at the level of the line of shafting L4.

The internal components of the reduction gear mechanisms 3 will now be described generally, whereupon the successive stages of the procedure for rendering the propulsion installation operative, and some specific phases of operation, will be explained.

In this connection, reference will be made to FIGS. 2 and 2a to 2b generally and, initially, more particularly to FIG. 2g.

On the line of shafting L2b, the top input shaft 2b drives a rotary coupling 16b and through this a shaft 17b extending into the bell 13b and bearing, inside said bell 13b, a clutch device 18b lockable in the engaged position by means of a dog clutch system 19b provided at the shaft end.

The driven, i.e. output part of the clutch 18b is connected to a tubular shaft 20b on which is secured a gearwheel 21b meshing with an identical gearwheel 21a which will be discussed hereinafter.

On the line of shafting L2a, the bottom input shaft 211 drives a resilient angular coupling 16a and, through the agency thereof, a shaft 17a extending as far as the bell 13a and bearing inside the latter a clutch device 18a which can be locked in the engaged position by a dog clutch system provided at the end of the shaft.

The driven, i.e., output part of the clutch 18a is connected to a.tubular shaft 20a to which there are secured the gearwheel 21a mentioned above and a gearwheel 22 meshing with the gearwheel 23 ekeyed on the output shaft 4 of the reduction gear (screw shaft line L4).

This system is completed as follows: on the top line of shafting L2b: by a starting gear 24b and a power take-off gear 25b, these two elements being connected to the driven part of the resilient rotary coupling 16b,

and, on the bottom line of shafting L211: by a starting gear 24a and a power take-off gear 25a identical to the above, these two elements being connected to the driven part of the resilient angular coupling 160.

In addition to the above-described elements which concern the main function of the reduction gear, i.e., the transmission of power from the power unit to the screw shaft, the said reduction gear comprises a number of auxiliary elements which have been referred to hereinbefore, and which are used during preheating of the power unit, during starting of the power unit, and during manoeuvres of the craft as low speed at ports. These other elements are controlled by the auxiliary engine 5 through the agency of the secondary input shaft 6a.

By means of a clutch 26 (see FIG. 2b), for example an electromagnetic clutch, and a bevel gear 26a, the secondary input shaft 6a drives the following:

Two horizontal tubular transverse shafts 27a and 27b respectively associated with the bottom engine unit 1a and the top engine unit 1b,

and a vertical shaft 28 permanently coupled to the said tubular transverse shafts 27a and 27b respectively by two bevel gears 29a and 29b.

As will be apparent from FIG. 2b, the top transverse shaft 27b bears the driving part of a dog clutch 30b, the driven part of which is connected to a shaft 31b extending through the tubular shaft 27b and bearing the freshwater pump 7b at one end and the oil pump 8b at its other end, these two pumps being associated with the top engine unit lb.

A second dog clutch 32b is provided on the same transverse line of shafting and is combined with the dog clutch 30b so that when one of these two dog clutches is in the operative position the other dog clutch is in the disengaged position, a neutral position in which both dog clutches are disengaged being provided in the control system for such dog clutches. The driven part of the dog clutch 32b is connected to a tubular shaft 33b co-axial with shaft 31b and driving a bevel gear 34b which will be discussed hereinafter.

As will be apparent from FIG. 2a, the bottom transverse shaft 27a is associated with elements identical to those described in connection with the top transverse shaft 27b, i.e., a dog clutch 30a, shaft 31a, a freshwater pump 7a, an oil pump 8a (these two pumps being associated with the bottom engine unit la), a second dog clutch 32a combined with the dog clutch 30a, and a tubular shaft 330 driving a bevel gear 34a which will also be discussed hereinafter.

As will be apparent from FIG. 2b, the bottom transverse shaft 27a is also coupled by a bevel gearwheel 35 meshing with the bevel gearwheel arrangement 29a to a vertical shaft 36 driving a secondary pump 37 for recovery of oil from the bottom of the reduction gear casing when only the auxiliary engine is in operation and, through a gearwheel 38, to a vertical shaft 39 driving a main pump 40 for drawing oil from the bottom of the reduction gear casing if at least one of the engine units laand lb is in operation.

The driven gearwheel of the bevel gear 34b (see more particularly FIGS. 2e and 211) is secured on a shaft 41 connected to a gearwheel 42 meshing with a gearwheel 43 connected to another larger-diameter gearwheel 44 meshing with a gearwheel 45 meshing with the power take-off gearwheel 25b already mentioned and belonging to the line of shafting L2b, the shaft of the gearwheel 44 rotating a fuel circulating pump associated with the top engine unit.

Similarly, and as will be apparent from FIGS. 2f and 211, the driven gearwheel of the bevel gear 34a is secured on a shaft 46 connected to a gearwheel 47 meshing with a gearwheel 48 connected to another largerdiameter gearwheel 49 meshing with the power takeoff gearwheel 25a already mentioned and belonging to the line of shaftinf L2a, the shaft of the gearwheel 49 rotating a fuel circulating pump associated with the bottom engine unit.

For the purpose of operating on the auxiliary engine 5 alone, the reduction gear 3 also comprises (FIGS. 2d

and 211) a bevel gear 50 driven by the vertical shaft 28, the driven gear wheel of this bevel gear being coupled by a gear train 51 to a shaft 52 bearing the driving part of a dog clutch 53, the driven part of which is secured to a tubular shaft 54 surrounding the shaft 52 and bearing at its end a gearwheel 55, the function of which will be described hereinafter in connection with the description of harbour manoeuvres.

To enable the reduction gear to be used for starting either of the engine units 1a and 1b, the gearing of the reduction gear is completed by a three-position transmission device or quadrant of the type which can pass from a neutral position to one or other of two end positions corresponding to coupling of the vertical shaft 28 (which is adapted to be driven by the auxiliary engine 5) to respectively the starting gearwheel 24a or the starting gearwheel 24b.

This transmission device (FIGS. 20 and 211) comprises a bevel gear 56, the driving gearwheel of which is secured to the vertical shaft 28 and the driven gearwheel of which is secured to a shaft 57 on which the driving part of a dog clutch 58 is secured for rotation, the driven part of the dog clutch 58 being connected to a tubular shaft 59 surrounding the shaft 57 and bearing at its end a gearwheel 60, the shaft of which forms the pivot for the support 61 of the quadrant of the gearing, of which the gearwheel is the input gearwheel.

In addition to the gearwheel 60, the gearing also comprises a gearwheel 62 meshing with gearwheel 60 and comprising a freewheel (the direction of which will be adapted to the starting problem to be solved), the driven part of which is connected to a gearwheel 63 meshing with a gearwheel 64 connected for rotation to a smaller-diameter gearwheel 65 meshing with an identical gearwheel 66.

For starting the bottom engine unit 1a, the support 61 is moved downwardly and the output gearwheel of the three-position transmission is the gearwheel 65 which then engages with the starting gearwheel 24b.

The various clutches and dog clutches mentioned above are individually provided with control systems which have been omitted from the drawing for clarity, and these control systems may be of a conventional type, for example hydraulic.

Also, all the gear trains in the reduction gear allow for the direction of rotation of the engine units and the direction required for the screw, and of course the entire system can obviously be adapted to different initial conditions as to direction of rotation by the addition of suitably arranged reversing gearwheels.

The successive stages of operation of the above propulsion installation will now be described starting from the time when the boat is at the quayside with the power unit cold until the time when the boat is in the normal operating condition with its power unit in operation, and this description will also include certain specific cases of operation.

For this description, reference will be made to FIGS. 3 to 10.;which have been made identical as regards the relative positions of the elements'(for simplification purposes), but in which those elements which are in motion have been indicated using double arrows and been given their reference numeral in order to distinguish the various stages of operation. The operations carried out on the dog clutches or clutches will also be indicated hereinafter in connection with each Figure.

l. Preheating (FIG. 3)

The boat is at the quayside with the power unit cold. A special heating installation (for example an electrical heating installation) is provided to heat the freshwater and oil involved in the propulsion installation. All the clutches and dog clutches of the reduction gear and of the three-position transmission are assumed to be in the neutral position.

Auxiliary engine 5 is started if it has not already been started for other purposes.

Dog clutches 30a and 30b are brought into the operative position.

Clutch 26 of auxiliary engine is brought into operative position.

In these conditions, the water pumps 7a, 7b and the oil pumps 8a, 8b and the secondary recovery pump 37,

are driven and the complete power unit heats up progressively.

2. Harbour Manoeuvre (FIG. 4)

When the preheating as described above has reached the required temperature, and before starting harbour manoeuvres or starting the propulsion engine, the previous manoeuvre must be interrupted for a moment to bring the various dog clutches concerned into the operative position without rotation.

Thus before starting the harbour manoeuvre procedure, clutch 26 is disengaged and when the gearhweels have stopped dog clutche 53 is engaged, and then clutch 26 is engaged so that while preheating is restored the gearwheel 21a coupled to the screw shaft is driven and thus receives all the power of the auxiliary engine but rotates at a reduced speed because of the internal step-down ratios of the reduction gear. In this stage ofoperation, the screw pitch is initially set to zero and is progressively brought to a suitable intermediate value.

In the specific case in which the harbour manoeuvre is not prior to a sea trip and is simply for a change of mooring position, there is no point in using the preheating stage, and in that case all that is necessary (FIG. 4a) is to leave the dog clutches 30a and 30b in the neutral position (the same applies to dog clutches 32a and 32b), and to bring clutch 26 into the operative position so that the boat moves at slow speed as before but without preheating.

3. Starting of top engine unit (FIG.

It will be assumed that the top engine unit lb is to be started first, preheating of the engine unit having been completed.

The screw is reset to zero pitch.

Clutch 26 is disengaged to stop the gearing.

Dog clutches 30b and 32a are brought into the operative position as is also dog clutch 58 which controls all the gearing in the three-position transmission 61.

The three-position transmission 61 is swung up to couple gearwheel 66 to starting gearwheel 24b.

Clutch 26 is engaged gently by successive pulses.

When gearwheel 24b has started, dog clutch 30b is disengaged by engaging dog clutch 32b.

Clutch 18b is brought into the operative position to ensure effective starting of top engine unit, the freewheel of gearwheel 62 then coming into operation, and then the three-position transmission 61 is returned to the neutral position.

4. Starting of bottom engine unit (FIG. 6)

If it is preferred to start the bottom engine unit 1a first, after the power unit has been heated to the required temperature as before, the screw is reset to zero pitch clutch 26 is disengaged to stop the gearing controlled by the auxiliary engine, the dog clutches 30a and 32b are brought into the operative position as is also the dog clutch 58 controlling all the gearing of the three-position transmission device 61, the device 61 is swung down to couple the gearwheel 65 to the starting gearwheel 24a, clutch 26 is engaged gently by successive pulses, when the gearwheel 24a has started the dog clutch 30a is disengaged by engaging the dog clutch 320, the clutch 18a is brought into the operative position so as to ensure effective starting of the bottom engine unit, the freewheel of the gearwheel 62 then coming into operation, and then the transmission device 61 is returned to its neutral position.

5. Operation of complete power unit (FIG. 7)

After the engine units la and lb have been successively started in the required sequence, clutch 26 is disengaged to disconnect the auxiliary engine 5, dog clutches 19a and 19b are brought into the operative position, dog clutches 32a and 32b being engaged, and the screw pitch is progressively increased by means of pitch control box 11.

In thses conditions, the total power of the two engine units 10 and 1b is transmitted positively to the screw shaft 4 and the auxiliaries associated with the said engine units (freshwater pumps 7a, 7b, oil pumps 8a, 8b, main oil recovery pump 40 and fuel circulation pumps) are effectively driven at normal speed.

6. Operation of botton engine unit alone (FIG. 8)

If it is proposed to propel the boat using only the bottom engine unit la (either because it is required to operate at half power or because the top engine unit lb has broken down or may be undergoing repair), the

dog clutch 19b is disengaged, and then the clutch 18b,

the dog clutches 32a and 32b being engaged and the clutch 26 remaining disengaged.

In these conditions, only the power of the bottom engine unit la is transmitted positively to the screw shaft 4 and only the auxiliaries associated with the bottom engine unit are effectively driven at their normal speed (freshwater pump 7a, oil pump 8a, main oil recovery pump 40 and bottom engine unit fuel circulation pump). 7. Operation of top engine unit alone It is it required to operate with just the top engine unit, three possibilities are available.

a. It is required to operate at half-power drive after preheating and starting the top engine unit alone by means of the auxiliary engine 5. In this case, after the procedure described under heading 3 (FIG. 5), dog clutch 19b is engaged and the screw pitch is progressively increased by means of the pitch control box 11.

b. Starting from complete operation of the power unit described under heading 5 (FIG. 7), the top engine unit 1b is required to operate alone, the bottom engine unit la being stopped just to use only half-power drive for the time being, the sequence of operations being as follows: the screw is reset to zero pitch, the two engine units are stopped after disengagement of the dog clutches 19a and 19b and then of the clutches 18a and 18b, starting of the top engine unit 1b alone is carried out by means of the auxiliary engine 5 as described under heading 3 (FIG. 5), and clutch 26 is disengaged and then dog clutch 30a is engaged at standstill.

In these conditions (see FIG. 9), only the power of the top engine unit 1b is transmitted positively to the screw shaft 4, the driven accessories being as follows for the top engine unit 1b; freshwater pump 7b, oil pump 8b, secondary oil recovery pump 37 and top engine unit fuel circulation pump and, for the bottom engine unit la: the freshwater pump 7a and the oil pump 8a.

c. If, on the other hand, after a total operation of the power unit as described under heading 5 (FIG. 7) it is necessary to carry out inspection, dismantling, or repair of the bottom engine unit (i.e., in a situation in which the operation of the bottom engine unit auxiliaries must be stopped the following procedure is carried 

1. A propulsion installation, comprising: a power unit; a reduction gear mechanism, a primary input shaft of the reduction gear mechanism drivingly connected with said power unit; an output shaft of the reduction gear mechanism arranged to drive propulsion means; wherein the improvement comprises the provision of: an auxiliary engine; a secondary input shaft of the reduction gear mechanism arranged to be driven by the auxiliary engine; means to decouple the said output shaft from the primary input shaft; said reduction gear mechanism including means to drivingly connect the secondary power input shaft to the output shaft with such output shaft decoupled from the primary input shaft; and means including a freewheel device to drivingly connect the secondary power input shaft to the primary input shaft for starting of the power unit, said freewheel device permitting transmission of torque from the secondary power input shaft to the primary power input shaft to rotate a shaft of the power unit in the direction in which such shaft is rotated for starting of the power unit in which the power unit comprises only two engine units, and in which the said means within the reduction gear mechanism for drivingly connecting the said secondary power input shaft successively with each primary input shaft comprises a transmission mechanism comprising a rocking support; a pair of driving gearwheels mounted on the rocking support, means to rock the support between three positions; and a pair of starter gear wheels arranged to be driven to drive their respective primary input shafts during starting of respective engines units; the rocking support when in a first said position thereof having a first of said pair of driving gearwheels in driving engagement with a first of said starter gearwheels, when in a third said position thereof having a second of said pair of driving gearwheels in driving engagement with a second of said starter gearwheels, and when in a second and intermediate position thereof having both of said pair of driving gearwheels out of engagement with said starter gearwheels.
 2. A propulsion mechanism as claimed in claim 1, and including pump means arranged to pump fluid to preheat the power unit prior to starting the same; means within the reduction gear mechanism being provided which can be selectively drivingly coupled with the secondary power input shaft for driving said pumps; gear means being provided in said reduction gear mechanism for drivingly connecting the pump means with the primary input shaft.
 3. A propulsion iNstallation as claimed in claim 2, in which the transmission ratios of the gears within the reduction gear mechanism are such that said pump means are arranged to be driven faster when being driven by said primary input shaft than when being driven by said secondary input shaft for the same rotational speed of said input shafts.
 4. A propulsion installation as claimed in claim 1, and including pump means operable during preheating of the power unit, said pump means being carried on and driven by the reduction gear mechanism.
 5. A propulsion installation as claimed in claim 1, in which the reduction gear mechanism comprises a casing having a joint plane at the level of each said input or output shaft of said reduction gear mechanism, whereby eventual power transmission components of said reduction gear mechanism may be simply exposed and repaired at each of its shaft levels.
 6. A propulsion installation as claimed in claim 5, and comprising covers provided in the walls of said casing at the end of each said input or output shaft, said covers straddling the joint planes of the casing.
 7. A propulsion installation as claimed in claim 6, wherein some of said covers comprise bell-housing which protect some of the components of the reduction gear mechanism. 